Other Parts Discussed in Thread: TMS320F28027F, LM5170, , LM5170-Q1
Hello,
im currently working on an bidiretional converter 12/48V 3KW 4phases. Im using the LM5170 as inner current loop compensator and want to use the TMS320F28027F Launchpad as outer voltage loop control.
The inner current loop controller is perfectly described by TI an the poles&zero placement is well documented for the transconductance amplifier.
But now to my problem:
I reverse calculated w_cp0 , w_cp1 and w_cz1 with:
B_0 = (T_s*w_CP0*w_CP1*(2+T_s*w_CZ1))/(2*(2+T_s*w_CP1)*w_CZ1);
B_1 = (T_s^2*w_CP0*w_CP1)/(2+T_s*w_CP1);
B_2 = (T_s*w_CP0*w_CP1*(-2+T_s*w_CZ1))/(2*(2+T_s*w_CP1)*w_CZ1);
A_1 = 4/(2+T_s*w_CP1);
A_2 = (-2+T_s*w_CP1)/(2+T_s*w_CP1);
and for B_0 trough A_2 i used the values in TIDA-01168 on Page 62. Ts = 1/48.828125 kHz
The results i got are for the buck:
w_cp1= 115048 rad/s = 18300Hz
w_cp0= 3662 rad/s = 582Hz
w_cz1= 750 rad/s = 120Hz
But how did TI calculated these values? Whats there compensation strategy? The Poles and Zero i calculated with the LM5170DESIGN-CALC.xlsx (avalible at TIs LM5170 page) are not even close the the values i reverse engineered. I'm looking for something like: Place w_cz1 at a fifth of the crossover frequency.
I would be realy thankfull for some help.
Kind regards,
Jochen Rohm